I thought I could gather some data sets I've come across that might be of interest to you.
I don't know if you already know about these, or if you have access to better ones and I havn't used them myself, save for the NASA blue marble, so I can't exactly say of what use they are. But anyway they might be of use for someone lurking this forum.
Land usage/land typeCollection of earth data setsBlue marble next generationAlso: Hi, this is my first post on the forum. I have been lurking unregistered for a while and was active on the
Infinity: Quest for Earth forum earlier. I have been interested in planet renderers, simulators and innovating game engine techniques and I'm very happy I bumped into your project. Good luck on the progress!